Tank cover



Aug. 3 1926.

L. A. BALDWIN TANK COVER Aug. 3 1926.

L. A. BALDWINl 1925 I 2 Smeets-Sheet Patented Aug. 3, 1926.

UNITED STATES PATENT OFFICE.

LESLIE A. BALDWIN, 0F ST. LOUIS, MISSOURI, ASSIG'NOR TO JOHNSJIANVILLE,CORPORATED, OF NEW YORK, N. Y., A CORPORATION 0F NEW YORK.

TANK COVER.

Application filed November 16, 1923. Serial No. 675,140.

This invention relates -to tank covers comprising insulating materialsand suitable for the roofs of out-of-door storage tanks for volatileliquids or lowpressure gases, or both, such as petroleum andrefinery-products tanks.

Liquids of the kind referred to when stored in metallic tanks of usualtypes are subject to evaporation losses of serious volume selectivelyadeeting the most valuable constituents of materials stored, especiallyduring such times as the tanks are subjected to Wide daily ranges oftemperature, to heavy Winds, or to excessive mean temperatures forconsiderable periods. The losses result from induced evaporation due topermitted changes in the surface temperature of the liquid and thetemperature ofthe vapors in the space above the stored liquid,

andV to convection and escape of the vapors; the freed vapors causeundue fire risks and odor nuisances.

The diurnal fluctuation of temperature in the vapor spaces of tanks ofthe kind referred to provided with the usual covers on sunny days hasbeen found to be of the order of to 60 Fahrenheit, with correspondingfluctuation of temperature of the surface of the liquid (petroleum) ofthe order of 10 to 20 F., Whereas the liquid at slx inches to a footbeneath the surface remains at a temperature fairly constant, having adiurnal fluctuation of the order of 1 to 3 F. only. A consequence of therising' and falling surface and vapor space temperatures is of courseexpansion and contraction of the collected vapors, With escape of thevapors through the necessary vent-pipes and the crevices of the coverduring expansion, and the intrusion of unsaturated air, capable oftaking up more vapor, during contraction. This phenomenon is commonlyreferred to as breathing in the oil industry. Typical cases of theselosses have been measured and computed by competent authority to reach1500 barrels annually, in the case 0f a 55,000 barrel tank holdingmidcontinent crude, with corresponding losses amounting annually to3,500 barrels in the case of 58 BaumeJ motor fuel, with some recessionfrom these values when tank-covers of certain types of metal or wood andmetal construction, newly installed, are employed the best practice thenresulting in annuai losses from average mid-continent crude of about 400barrels and of about 750 barrels for motor-fuel. Losses as low as theseminima are sel-dom attained in actual practice, the expansion ofwallsand cover and the filling and emptying stresses on and motions of thetank walls resulting inevitabl in crevices into and from which thewindy-V draft of air and vapor is substantial and costly. The storagelosses in practice, especially of the gasoline fraction, maybe assumedto average from three to four per centum.

Anobject of this invention is to provide for minimizing or preventinglosses of stored liquids by evaporation or the ex lansion and escape ofgases or vapors w ich may accumulate in the vapor space over the surfaceof such liquids, and for this urpose the invention provides a genus ofeat refleeting and heat insulating gas-tight covers adapted for use withliquid storage tanks 'to cause the internal temperature of the contentsof the tank to be maintained relatively constant and to prevent escapeof vapors.

For example, the invention is exemplified by and will be described asapplied to gastight heat-insulating roofand cover constructions adaptedto enclose the tops of the storage tanks or chambers to be protected. toextend over the connections between'the roof and the side -wall of thestorage tank, and to be joined to the side, walls of the tank by agas-tight expansible joint, and having features causing all joints andconnections to be gas-tight and weather roof, enabling the heatinsulation to be ma e impervious to gases and liquids, and permittingthe outer surface, if desired, to reflect radiantgheat, lwhilepreventing the substan tial transmission of heat or passage of -gasesthrough the cover. The new cover is applicable to existing tank roofconstructions.

In the instances of embodiments of the in vention adapted for use withoil storage tanks illustrated in the accompanying draw- .ings

Fig. 1 is a vertical section representing a typical. application of theinvention to an oil storage tank having a Wooden roof;

free joint between roof and walls.

Fig. 2 is a similar vertical section. representing a modificationapplied to ancil tank having a sheet or plate metal roof; and

Fig. 3 is a detail vertical section at one of the joints between theadjacent sheets of insulation according to the construction of Fi 2.

n the drawin Fig. 1 shows at 1 the side wall of an oil-tank of the usualcylindrical riveted-sheet metal type upon which the ordinary wooden roof2 1s supported :by wood rafters or steel beams 3, in the common way.Attached to, and projecting over the edgeof said roof are fastened bymeans of broad-headed nails a sheets 6 of suitable material, forexample, compressed libre board, metal, wood, or asbestos-wood, havingtheir outer edges bent downwardly into a curved portion 7 These sheetsmerely rest upon or 'extend just above the rimstiening metallic cornice1* of tank wall 1, and here provide the necessary slidingTgr e sheets 7also support the overhanging flexible eaves sealing extension of the roocover and prevent its becoming abraded or too sharp y iexed at the edgeof the roof. Joints at this place have heretofore provided a lar eleakage space, whatever type of cover may ave been employed for theremainder of the wooden deck 2.

According to the present invention, a cover of s-tight and weather-proofmaterials having a flexible and slack eaves-section'to serve as anexpansion joint is built in place about the top of the tank and on thedeck 2. Preferred materials for this cover are l f laminated fabricswhose rincipal thickness is comprised of a non-con uctin felt or mat ofsuitable fibrous texture, suc as one or more sheets of a felt or bat ofthe well-known heat insulation materials, for example feltedcattle-hair, asbestos, wood-fibre, vegetable fibre, mineral wool, cork,wool,cotton, diatomaceous earth, marsh ass or other or mixed coarselibres, not ereinv claimed as new. The recommended material is awellknown fabric made up of a felted mat of cattle-hair with or withoutadmixtures, enclosed between strong paper covers. For the purposes ofthe present invention, one of these covers is an asphalt saturated paperand the'other cover is impre ated with sodium silicate in aqueous soution, or with` any other satisfacto flexible gas-resisting impre ant,"to lill interstices and aid in rendermg the aggregatelaminated fabricimpervious to gases. At the eaves this felted layer or layers isexteriorly protected and rendered impervious to gases and water by oneor more layers of impervious canvasasphalt, asbestos-asphalt, or otherflexible sheet 9, lpreferably com rising a li ht canvas, clot ofasbestos res, a flex-i' le fabric or an asbestos or other feltimpregnated .by a layer of weather-resisting wall 1 of the tan withmelted hard asphalt, fastened to the outside layer of insulating fabricorfelt by suitable fusible cement, preferably consisting of the sameasphalt as the impregnant. This layer may in turn be rotected by a layer29 comprising an asphalntic binder and mineral in edients, such asasbestos and any suitable fi ler, for example, sand, calcined oruncalcined powdered stone lime, ground calcareous matter or the like;Aut in the preferred construction, the greater part of the exposedsurface of the roof, for example, the roof slope above line A, isfinished by one or more lagers of impervious water-laid asbestos-asp altsheets 32, (or other asphalted sheets, such as rag-felt sheets) followedwhite material 37, conveniently applied y attaching by suitable fusiblecement, preferably asphalt to the upper-surfaces in overlappingrelation, sheets of water-laid asbestos felt impregnated'with asphalt ontheir under sides Iiil order to construct this type of cover, therecommended procedure, referring to Fig. l, is first to apply about thetop of the .in a line substantiall horizontal, a layer 11 of suitablecementitious adhesive, such as melted asphalt, into and by which thetop'edge only of a strip of the impervious canvas asphalt, asbestos-.asphalt or other flexible fabric 9 is firmlyl embedded, any verticalseams being lapped and cemented. The strip 9 now hangs down from itshorizontal upper edge and is washed over with a coating of meltedasphalt 8, upon which is applied a layer 12 of the insulation fabric,which is 1n turn brushedwith asphalt, and a wider strip for a layer 13of the insulation felt applied.

The belt of laminated material thus built about the cylindrical wall lis now reinforced to plrevent breaka e of its gas-tight contact wit thewall 1 y motions of the tank, wind or internal pressure. A preferred wayof doing this is to encircle the whole tank and the applied fabric witha suitable compression binding, such as a metallic strip,

or, as shown, two or more runs of strong -per edge of the felt layer 19with any suitable cement, such as silicate of soda. This keeps gases oroil out of the edges 14 of the 'cover material.

The eaves-plates 7 having been applied, the free lower edges of strips9, 12 and 13 are now brought up over the edge, and severilo old theapplied l ally fastened. The wider strip 13, which is preferably taperedin thickness to its edge 16, may be fastened to the wood deck with flatbarbed nails 21 driven through flat metal caps 22. The edge 17 of thesheet 12 is similarly fastened, and forms a seat for the abutting edgeof the next strip 18 of the felt material. The entire roof may becovered with two or more layers of the felt insula tion material laidwith broken joints, but in the usual case two layers at the eaves andone on the roof slope are suliicient. The insulation sheets 13, 18 etc.may be laid in an asphaltic cement if desired, but in the usual casethis is not necessary, the outer layers of the roof providing asuiiiciently impervi ous structure.

rlhe outer layer 9 at the eaves is laid, preferably over the layer ofinsulating felt material 12 and over the ioint at' edge' 17, in aliberal coat 3l of hot asphaltic cement and nailed at 21. v

The roof slope to the break of the eaves at A is now covered withoverlapped sheets of the water-laid asphalt impregnated asbestos fclts,rag felts or other rooting sheets 32, laid in hot asphalt and preferablynailed frequently to the substructure through caps 22; over this, inlayers. 31 of melted asphalt or asphaltic cement, a furtherweather-proofing and heat insulating layer 37 of sheets or strips ofasbestos felt, rag felt or other felted roong sheets, preferably alread.impregnated on its under face only with t e asphal- 2 tic impregnant,and preferably white on its exposed surface, is now laid to the line A,

joints in this being overlapped, as at 38.

.The cover is completed by applying a relatively thick layer 29 of theplastic asphaltic cement, from the line A to the down-hang of the eaves,from which rain water dri s clear of the tank from the curved portionwhich ilexes slightly to accommodate the motions of the tank shellrelative to its roof and cover.

Referring now to Fig. 2, tanks having metal roof-decks 43 may beprotected according tothe same principles, with variation of the mode ofattachment of ,the protective cover. An impervious strip or sheet 47,preferably of the canvasfasphalt, the asbestes-asphalt or otherflexible' fabric material, is first fastened to the cylindrical wall 41near the top by a belt of asphaltic cement 44 applied to the wall, andis then coated with a layer 46 of cement or melted asphalt, into whichthe lower edge of a relatively stiif sheet 49 of impregnatedasbestosfelts,.asphalt saturated rag felts or a combination of both or othersuitable material is embedded. Sheet 49 may be a flashing felt ofwell-known construction; any flexible protective material capable ofsupporting the remainder ofthe eaves section of the protective roofagainst the cutting and rubl bin stresses of the tank edges is suitable;a

after the impregnated strip 47 is attached at 44. A strip 51 of theabove described in- Sula-ting felt sheet, preferably having' an edgetapered at 54, is now applied in a layer of hot asphalt 'at 52 and at52, this strip beingof sufficient width to have its edge reach theillustrated position when bent over Vthe sheets 49. Upon the strip 51,in a layer of hot asphalt, a second strip of insulation felt 53 is nowlaid; and a binding 'wire 56 may now be wrapped about the tank to holdthe lower edges of the insulation felt and form a guide, about which theimpervious-- fabric strip 47 is now turned up andy over into a layer ofhot asphalt 61. The layer 61 may extend over the down-hung part of sheet53, but preferably the cement layer 43 on the now inner face of strip 47is supple*- mented by a cementitious coat on this downhung art of thesheet 53, the hot asphalt layer eginning under the circumferential lineB.

The strip 47 is wide enough to overlap the inward edge of the strip 43,and is sharply bent downwardly and then inwardly at 62 for attachmentdirectly to the deck 43 by a layer of asphalt 55, and thus provides aseat for the abutting edge of the next strip 57 of insulation felt. A

At each radial and circumferential joint of the strips of insulation-felt 57, it is preferred to attach thetupp'er edge of the outer stripin this manner, as shown in Fig. 3,V in which a narrow strip 65 ofthecanvas' asphalt, asbestos asphalt or other flexible fabric materialis shown as applied to the top of an outer or lower strip, and bentdownward at 59 and inward at 56, to form a seat' for the lower or outeredge of a felt strip 57. All crevices in this construction are filled at58 with the attaching asphalt or a cement.

From the circumferential line B the remainder of the cover is built upof asphalt proof cement 70, referably the same material above descrilayer 29, Fig. 1.

To accommodate varying conditions of d or preferred for' the 115impregnated asbestos felts, rag felts or other tank structure it will beunderstood that the constructions exemplified by those shown in Fig. 1or Fig. 2 may be interchangeably resorted to in whole or in part,depending upon the structure of the tank, to construct covers for woodor steel deck tanks of different kinds.

It will be understood that the elements of the improved cover aresufficiently ductile and extensible to enable them to be applied toconform to the large circumferential circles of the tank top withoutdifiiculty, but for small tanks, the materials employed may comprisesheets lapped frequently at radial joints to permit edges of the sheetsto lie on chords of the circles defined by their assembled positions.

In each instance of the invention, the necessary hatches and vent pipesmay be sealed around by the cover materials. or otherwise, in order toassure a vapor-tight heat-resisting construction. At least one vent pipeis necessarily left open to prevent any considerable linternal pressurefrom building up. .But with eflicient heat and wind insulation andsealing,`as herein provided, the large breathing or diurnal expansionlosses and the wind-drift losses are so nearly prevented by preventionof rapid variation of the internal temperature and eicient sealing thatthe output ofvapor through the ventpipe is reduced to a mere seasonalloss,- during rises of the mean temperature, and such incidents as theloss of lvapor during filling of the tank. These gf losses are notserious in volume or frequency.

It will be observed that this invention-provides a sealing andinsulation cover capable of being applied to all types of existing tanksand serving to cause the interior temperature to be maintainednearlyconstant under diurnal temperature changes, and capable of resisting theeffects of relative movement of the parts of the tank `which haveheretofore resulted in of vapors.

I claim v 1. The combination of a tank having a roof and a Wall with aflexible cover adapted to seal spaces between the tank roof and its wallcomprising a heat insulation layer and laminas of paper resistant to thepenetration of hydrocarbon vapors, and having a lamina of a water-proofheat-resistant fabric mterpenetrated by a continuous asphalticinclusion.

2. A tank of the kind having a wall and a roof, and having a flexiblecover ada ted to seal spaces between the tank roof an its wallcomprising a heat insulation layer and laminas of paper resistant to theenetration of hydrocarbon vapors, and having a. lamina of a water-proofheat-resistant fabric interpenetrated by a continuous asphalticinclusion, and a lamina having a Whlte exterior face.

3. A roof construction for tanks comprising a flexible cover adapted toseal spaces between the roof of a roofed tank and its wall comprising aheat insulation layer and lamin of paper resistant to the penetration ofhydrocarbon vapors` and having a lamina of a water-proof heat-resistantfabric 'interpenetratedby a continuous asphaltic inclusion, and a laminahavin 1 a weather-resistant white exterior face o asbestos fibre.

4. A flexible cover adapted to seal spaces between a tank roof and itswall com rlsing a heat insulation layer and laminas o paper impregnatedwith a flexible saturant adapted to render-the paper resistant to thepenetration of hydrocarbon vapors, and having alamina of a water-proofheatfresistant fabric interpenetrated by a continuous asphalticinclusion. .V f

Signed by me at St. Louis Missouri this First day of November, 1923.

LESLIE A. BALDWIN.

leakage and loss

